This invention relates to a digital recording apparatus applicable to such as a digital audio tape recorder (hereinafter abbreviated in a DAT).
Table 1 shows the values of a sampling frequency, a clock frequency for signal processing, a drum rotating speed and a tape speed in each mode of a conventional DAT (a rotary-head digital audio tape recorder) and the DAT of the present invention.
Firstly, in the case of recording in the conventional industry standard mode, a magnetic tape is transported at a standard speed of 8.15 mm/sec and a drum provided with a pair of rotary heads is rotated at a standard speed of 2000 r.p.m.
Analog input signals such as audio signals of two channels L and R, are converted to Pulse-Code Modulation (PCM) data of 16-bit quantization by A/D conversion with a sampling frequency of 48 kHz.
The PCM data are processed with specific data processing, modulation, etc. with a clock frequency f for signal processing.
The processed data are alternately supplied to the pair of rotary heads to be recorded on an inclined track being formed on a tape.
In the case of reproducing, reproducing signals generated by the rotary heads with the standard drum rotation speed and tape speed the same as in the case of recording are demodulated and decoded with the clock signal f to be the original audio signals.
Furthermore, the case of recording in the long play mode of the well known DAT in which the recording time is two times longer than that of the standard mode for the same length of the tape will be explained.
In this case, the sampling frequency is set to be 32 kHz, and the drum rotation speed and the tape speed half of the standard mode, respectively.
The PCM data of 16-bit quantization which are converted by A/D conversion with the sampling frequency of 32 kHz are converted to be 12-bit quantization data by nonlinear quantization so as to maintain the dynamic range. After the conversion, the 12-bit data are processed by specific signal processing.
In the case of reproduction, the clock frequency and the tape speed are set to be half those of the standard mode, and the drum rotation speed to be the same as that of the standard mode.
Next, it will be considered to perform double-speed dubbing with the aim of halving the recording time by combining the DAT with such as a compact disk (CD) player. In other words, it will be considered that the CD player performs double-speed reproducing to reproduce audio signals whose transfer speed is two times faster than the normal reproduction speed and the reproduced audio signals are supplied to the DAT to conduct high-speed recording.
In order to perform recording by such a method and reproducing of the recorded signals with normal speed by the conventional DAT, the frequencies and speeds are set as follows.
In the case of recording, the sampling and clock frequencies and also the drum rotation and tape speeds are set to be double of the standard mode, that is, 96 kHz, 2f, 4000 r.p.m. and 16.3 mm/sec, respectively.
In the case of reproduction, the clock frequency and also the drum rotation and tape speeds are the same as those for the standard mode.
In the conventional digital recording apparatus explained above, the maximum signal processing capabilities required in each of the standard, long play and double-speed modes to perform recording are calculated as follows.
the standard mode: 48 kHz.times.16 bits.times.2 channels=1536 kbits/sec PA0 the long play (.times.2) mode: 32 kHz.times.12 bits.times.2 channels=768 kbits/sec PA0 the double-speed mode: 96 kHz.times.16 bits.times.2 channels=3072 kbits/sec
Therefore, double-speed recording by means of the conventional digital recording apparatus results in large capacity-signal processing circuits which leads inevitably to an increase in cost.
TABLE 1 __________________________________________________________________________ CONVENTIONAL DAT DAT OF DOUBLE THIS INVENTION STANDARD MODE LONG PLAY MODE SPEED MODE HIGH SPEED MODE RECORD- REPRO- (time: .times. 2) REPRO- RECORD- REPRO- (speed: REPRO-. 2) ING DUCING RECORDING DUCING ING DUCING RECORDING DUCING __________________________________________________________________________ SAMP 48 kHz 32 kHz 96 kHz 64 kHz FREQ CLOCK FREQ f f f/2 f/2 2f f f f/2 FOR SIGNAL PROCESSING DRUM 2000 2000 1000 2000 4000 2000 2000 2000 ROTATING r.p.m. r.p.m. r.p.m. r.p.m. r.p.m. r.p.m. r.p.m. r.p.m. SPEED TAPE 8.15 8.15 *4.075 *4.075 16.3 8.15 8.15 *4.075 SPEED mm/sec mm/sec mm/sec mm/sec mm/sec mm/sec mm/sec mm/sec __________________________________________________________________________ *A tape speed is half that of the standard mode.